Illumination is the basic need for the human kind. In recent years, with the surge of the global economy and the commercial activity, the electricity utility for illumination has been boosted. Therefore, the overall demands of illumination are considerable. The low-pressure gas discharge lamp is by far the most widely used lamp. The gas discharge lamp is also known as a fluorescent lamp or a daylight lamp. Therefore, if the energy consumption of the low-pressure gas discharge lamp can be reduced efficiently, a considerable amount of electricity can be saved. With the evolvement of time and the promotion of living quality, the conventional drivers for driving illumination device have been outdated. Therefore, the electronic ballast which is featured by low electromagnetic interference, high efficiency, high power density, zero flickering, light weight, high-quality illumination, and high energy-saving performance, have become the mainstream of illumination device.
The electronic ballast used for illuminant purpose has a complex circuit structure. The conventional single-output electronic ballast includes an AC/DC converter and an inverter. In operation, the AC/DC converter converts an AC input voltage into a high DC voltage, which in turn is converted by the inverter into a high-frequency AC output voltage for driving the gas discharge lamp. The AC/DC converter may possess a power factor correction function for boosting the power factor of the electronic ballast. The inverter is able to provide illumination with high efficiency, zero flickering, and high quality through the regulation of operating frequency.
Nowadays, a vast amount of fluorescent lamps are widely used for indoor illumination in a spacious place such as a warehouse. When fluorescent lamps are used in daylight situations, outdoor situations with sufficient lighting, or indoor situations without operators, part of the fluorescent lamps may be turned off to avoid the waste of energy and save energy consumption.
To meet the goal of selectively turning off part of the fluorescent lamps, a multi-output electronic ballast has been proposed for driving two lamp assemblies. The conventional multi-output electronic ballast includes a first AC/DC converter, a second AC/DC converter, a first inverter, and a second inverter. The first AC/DC converter has a first input terminal and a first output terminal. The first output terminal of the first AC/DC converter is connected to the first inverter, and the power circuit consisted of the first AC/DC converter and the first inverter is used to drive the first lamp assembly. Likewise, the second AC/DC converter has a second input terminal and a second output terminal. The second output terminal of the second AC/DC converter is connected to the second inverter, and the power circuit consisted of the second AC/DC converter and the second inverter is used to drive the second lamp assembly.
In order to allow the user to control whether the second lamp assembly is illuminating or not, a first external switch is connected in series with the first input terminal of the first AC/DC converter and a second external switch is connected in series with the second input terminal of the second AC/DC converter. In this manner, the input voltage can be manipulated to be selectively applied to the first AC/DC converter and the second AC/DC converter by the switching operation of the first external switch and the switching operation of the second external switch. As a result, the external switches can be used to selectively turn off the fluorescent lamps.
As each power circuit for driving the lamp assembly is independent from each other, the multi-output electronic ballast must possess a plurality of AC/DC converters. Furthermore, the AC/DC converter includes a plurality of expensive electronic components. Hence, the conventional multi-output electronic ballast is bulky and expensive.
It is therefore needed to develop a multi-output electronic ballast with small size and low cost.